Abstract
Particle size is one of the most important requirements for the successful implementation of magnetic nanoparticles in numerous scientific and engineering applications. Here we proposed the use of low-gradient magnetic separation (LGMS) technique for size fractionation of magnetic nanoclusters (NCs) due to its ease of implementation. Poly(sodium 4-styrenesulfonate) (PSS)-grafted iron oxide NCs, with excellent colloidal stability needed for most environmental engineering applications, were employed as a model system to test the effectiveness of our separation strategy. Results showed that successive reduction in average hydrodynamic size and sample polydispersity was achieved after going through LGMS. This size-selection process is independent of initial particle concentration and gives consistent results over a broad range of particle concentration (from 0.025 g/L to 10 g/L). By fine-tuning the externally applied field strength from similar to 4600 to similar to 1100 gauss, we observed a well-characterized, predictable separation behavior which can be rationalized based upon our understanding of low-gradient magnetophoresis. In addition, we found that the time-dependent magnetophoresis profiles of PSS-grafted iron oxide NCs registered dissimilar behavior as compared to its bare counterpart, at which the latter is more concentration-dependent than the previous ones. Occurrence of size fractionation-based magnetophoresis is believed to account for this variation.